First prepare the shortcrust pastry: combine softened butter, sugar, salt and egg yolks in the bowl and mix until creamy, then add milk, vanilla and flour and mix quickly to obtain a smooth mixture.
Divide the dough in half and incorporate the coffee into one of the 2, kneading quickly: for a more uniform colour, once the coffee has been incorporated, let the dough rest at room temperature, then knead it again.
Wrap each of the two loaves with cling film and let them rest in the fridge for at least 30 minutes.
Separately, roll out the light and dark shortcrust pastry with a rolling pin on a lightly floured work surface, creating sheets of about 0.5 cm.
Take 2 cutters of your choice (I chose a scalloped round and a small heart, but anything will do, as long as one of the two is much smaller than the other) and create your biscuits with the large cutter, then create your biscuits with the small one. a decoration in the center of the biscuit.
Do the same thing with both shortcrust pastries, then delicately insert the light hearts into the dark biscuits and vice versa.
Place the biscuits on the baking tray lined with baking paper (or lightly greased) and cook for around 10-15 minutes (12 was enough for me) at 180°C, in a pre-heated static oven.
The two-flavored biscuits are ready, at least let them cool before serving.
